1. Field of the Invention
The invention concerns self-adhesive acrylate copolymers, a process for their preparation as well as an especially favourable use of these acrylate copolymers.
2. Background of the Related Art
Self-adhesive substances or also pressure-sensitive substances are permanently tacky substances, which adhere spontaneously to many surfaces of different materials on light pressure. Such pressure-sensitive substances are almost exclusively used for the coating of webs, such as paper or film, adhesive labels or self-adhesive decorative films. Important properties of the pressure-sensitive substances are for example their adhesion capacity, their heat, ageing and softener stability.
From U.S. Pat. No. 3,691,140, adhesive elastomer acrylate copolymers are known in the form of micro-spheres. These microspheres are produced by aqueous suspension polymerization. The micro-spheres which are obtained after polymerisation are dispersed in solvents, whereby suspensions are obtained. After the application of such a suspension on a web to be coated, the solvent is evaporated, so that a coating of these acrylate copolymer micro-spheres results on the web. This coating has an adhesive effect, so that the web thus coated can be used, for example, for covering or protection of sensitive surfaces. Furthermore, these coated webs have the desirable property that they can be used repeatedly and can repeatedly be removed from a surface to be protected, without this deteriorating effect on the adhesion or adhesive properties. However, this known type of copolymer suffers from the disadvantage that its adhesive properties gradually decrease with time, so that finally no adhesion can be achieved. This is because of a migration of the micro-spheres from the web on which they are applied, to the surface which is covered by the self-adhesive web.
For this reason, this type of adhesive substance was further developed in accordance with U.S. Pat. No. 3,67 ,731 (or the corresponding DE patent 24 17 312) so that in addition to the micro-spheres of acrylate copolymer, a binding agent layer is provided on a web which is to be coated. This binding agent layer, which contains micro-spheres, is applied so that one part of the micro-spheres protrudes from the binding agent layer and thus can come into contact with a corresponding material onto which it should adhere.
It is an object of the present invention to provide an acrylate copolymer which has good and long-lasting adhesive properties. In particular, their properties should not themselves alter disadvantageously when repeated adhesion and removal is undertaken from materials to be secured. In addition, the invention also has as an object a process for the preparation of such acrylate copolymers by simple means and methods.